Research On Optical Image Encryption Based On Double Random Phase Encryption

With the dramatic advancement of information technology,the security of information is becoming significantly important.One of the most common expression of information is digital image,so the security of the transmission has attracted more and more attention.In recent decades,optical image encryption techniques can offer fast parallelism and large capacity,and proposed a promising tool for information security through using larger key space of freedom,which makes optical methods to encrypt images more quickly and efficiently,and now it has widely used in the field of information processing.In recent years,a lot of systems of image encryption have been proposed at home and abroad,but still in the stage of exploration and experimentation.So it is significant to conduct more in-depth research in system.This paper studies on double random phase encoding based on fractional Fourier transform technology,which is combined with image scrambling technology,theta modulation and asymmetric encryption systems,consequently,the system's security has been enhanced.First of all,we introduce the basic theory of optical encryption.Then,we discuss the double random phase encoding in the fractional Fourier domain,and analyze the limitation of the system by computer simulation.And discrete multi-parameter fractional Fourier transform(DMPFRFT)applying in image encryption is studied,with image scrambling technology,it turned out that the key space can be expanded and the system stability can be improved.Secondly,theta modulation is introduced,we design a multiple-image encryption system based on theta modulation and DMPFRFT.After shifting the spectrum center to other position by respective amplitude grating for each image,a complex signal can be obtained,next complex signal is performed by image scrambling technology and DMPFRFT to obtain the encrypted image.The decryption process is an inverse of the encryption process,these images can also be decrypted by using the keys,such as phase only matrixes and the coefficients for DMPFRFT.Finally,we have shown that the traditional double random phase encryption system is symmetric and has its own limitation: one is that it has inherently linear nature,resulting in the system is vulnerable to attack;another is because the system's security depends primarily on the key security,it is necessary to make sure the key change between sender and receiver method is reliable,meanwhilepreventing key leak.The above mentioned two points make the system have a security problem,so the asymmetric image encryption algorithm based on phase truncation discrete multi-parameter fractional Fourier transform is studied to provide higher security.And simulation had been performed to validity the robustness and security of the proposed schemes.